Nerve growth factor (NGF) is necessary for the growth and development of the sensory and sympathetic neurons. The mechanism by which this occurs is now beginning to be uncovered. The purpose of the project is to look further into the structural and functional relationships of NGF. We want to look at NGF binding and internalization with respect to both sensory and sympathetic neurons at physiological concentrations. To develop a new bioassay which is more quantitative than the present ones. To determine more about the active site or portion of the beta NGF molecule and try to synthesize that portion of the molecule. Also, to investigate further the molecular species of NGF which are present at physiological concentrations. The binding interactions and internalization of NGF with sensory neurons will be investigated using 125I-beta NGF. Internalization will be assessed by incubation of sensory neurons with 125I-beta NGF and treated with trypsin. The trypsin non-releasable counts will be determined and used as a measure of internalization. Chick embryos will be cultured outside the egg shell which will allow for a much easier access for injection of various concentrations of NGF. After the injections, tyrosine hydroxylase levels will be determined either in the sympathetic chain ganglia or in the superior cervical ganglia. The active site of the beta NGF will be further investigated using proteolytic cleavages which cause inactivation, finding where that portion occurs along the chain and chemically synthesizing that portion. This chemically synthesized portion and any other peptides which are produced from proteolytic cleavages will be tested for biological activity and in competition studies against native beta NGF. The molecular species present at physiological concentrations will be determined by gel electrophoresis, biological activity and immunological assays. To determine the importance of 7S NGF and any intermediate complexes which are formed between beta NGF and the other two subunits of 7S NGF.